Updating a file with new input

Question

Hi. How would I be able to read in a file, and than update that same file with input from the user? Example: I have a file named 'Num' with the numbers '1','2', and '3' in it. How could I read those three numbers in, and than update it the file with something the user puts in, like '4'? Thanks.

Answer 1

import java.io.*;
public class ReadAndUpdateFile
  public static void main(String args())
    throws Exception
    new ReadAndUpdateFile(args(0));
  } // main
  public ReadAndUpdateFile(String file)
     throws FileNotFoundException, IOException
    String line = null;
    BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
    while ((line = br.readLine()) != null)
      System.out.println(line);  // dump each line
    br.close();
    System.out.println("Enter your number:");
    br = new BufferedReader(new InputStreamReader(System.in));
    line = br.readLine(); // Get User Input
    boolean append = true;  // True means that it will append to the file
                            // if it exists and create it if it doesn't
                            // set to false it will overwrite it with a new file
    FileOutputStream fos = new FileOutputStream(file, append);
    fos.write(line.getBytes());
    fos.flush();
    fos.close();
  } // ReadAndUpdateFile
} // ReadAndUpdateFileOK... this gives you a VERY good idea... read the javadocs to understand it
PS I didn't compile it... so it may not compile.. but it is VERY close...